Cold crash question

So I am cold crashing for the first time , and the airlock is moving in reverse sucking air back into the carboy. I understand the physics of it but don't like it. It is obviously sucking air with O2 back into my carboy. I suppose since CO2 is heavier than air, there will still be a blanket of CO2 over the beer to stop oxidation but it feels wrong. Any opinion/experience out there. Should I have done something else?

Thanks, t

How much air depends on the amount of headspace.

Air on average will lose about 4cc of volume per liter for each 1 degree drop in temperature.

If you have 1 liter of headspace in your carboy and reduce the temperature from 65 to 35 you will be sucking in about 120cc (4ounces). As to the effect this will have I do not know.

Less headspace means less suck back.

Hope this helps??

bosco

I think the whole "blanket" thing is a myth, and the air will diffuse into the CO2/vice versa, which supports the notion of keeping a minimal headspace.

Cheers!

i started using a solid bung to plug the lid in my bucket when I cold crash

i left the airlock on for many batches though and never noticed any oxidation etc, 5.25gal batch in a 6.5gal bucket